An anterior capsulotomy procedure is one wherein the surface of the anterior capsule of the eye is broken or partially removed allowing access to the lens interior of the eye. Such a procedure is commonly performed as part of a cataract removal. The current surgical procedures for anterior capsulotomy include the Christmas-tree technique, the beer-can opener technique, etc. See F. H. Davidtorf et al, Atlas of Eve Surgery and Related Anatomy, Keller Publishing Company, pp. 29-34, 147-166, Vol. 128, No. 305 (1978). These techniques are deficient, however, since they produce flaps of anterior capsule material, called tags, which remain to obscure the surgeon's view of the capsule and can interfere with the removal of the lens and/or cortical material and the placement of an artificial lens. The tears produced by these procedures can also allow an implanted artificial lens to slip or escape entirely from the capsule.
Cauterization techniques have also been employed for surgically entering a lens capsule in the course of a cataract operation. See S. Polar, U.S. Pat. No. 4,301,802. Polar discloses a cauterizing tool in which the localizing working surface of a cauterizing electrode is at an offset end of an elongate tubular body which may be of hypodermic needle proportions. Cauterization devices, such as Polar's, permit an electric current to be passed between the electrode and a receiving electrode contacting a patient's body elsewhere. The current coagulates the anterior capsule, making it extremely friable. Although cauterization techniques minimize the number of tags and tears, these devices can produce capsule shrinkage and rupturing and adjacent zonules due to excessive heat produced by the electrode. Additionally, this equipment is more expensive than mechanical cutting devices and can produce electrical interference in electrical monitoring equipment in the operating room.
There are commercially available cystitomes that do not produce capsule shrinkage. See Geuder, German Patent No. 3205959, issued Sept. 1, 1983, and Schmidt, European Patent Application No. 165657. The Geuder patent discloses an instrument employing a cutter which operates via a wire system within a lance to make a desired incision. Schmidt discloses a rotating stylus cystitome having a knife blade configured in an offset manner, whereby the blade cutting edge is spaced from and directed toward the blade pivot axis, thereby providing a castering action of the blade in response to movement of the shaft tip. See also J. C. Witzleben, Describe New Method, Surgical Knife for Anterior Capsulotomy, Reprinted from Ophthalmology Times, Vol. 9, No. 18, Sept. 15, 1984.
The rotating stylus cystitome, in its earliest configurations, has presented some difficulties during surgery, since the crimped end of the rotating cutting member can often bind and occasionally cause the stylus to fail to rotate completely. This has been attributed to the fact that the rigid shaft or cannula member is round and the rotating stylus tends to follow the curvature of the hole in the round cannula in which it is disposed. The sliding metal surfaces of the shaft and stylus can cause the rotating stylus to move vertically up and down as it is rotated. In addition, the angle between the faces of the cutting blade has often been too large to provide clean and efficient cutting of the anterior capsule, especially when the cutting blade is significantly deviated from a position perpendicular to the plane of the capsule.
Accordingly, there is a need for an improved cystitome having a construction which provides for efficient cutting of the anterior capsule for cataract operations. There is also a need for a rotating stylus cystitome that provides smoother rotation during surgery.